Activated Protein C Antibody
Protein C is a vitamin K-dependent serine protease produced in the liver and made up of 2 polypeptide chains. The 62kDa proenzyme is activated by thrombin and the active enzyme cleaves factor Va and VIIIa and thus inhibits blood coagulation. The molecular weight of the active enzyme is 55kDa and the normal concentrations in human plasma is approximately 1-3 ng/ml because of the very fast turnover, the proenzyme concentration is approximately 3 µg/ml. The activated protein C (APC) is inhibited by members of the serine protease inhibitor (serpin) family, of which alpha1-antitrypsin (AAT) and protein C inhibitor (PCI) are the most important. This antibody is specific for a conformation-dependent neoepitope that is expressed in activated protein C upon complex-formation with alpha1-antitrypsin. No reaction is seen to non-complexed alpha1-antitrypsin and weak cross-reaction with protein C zymogen. The antibody specificity is calcium dependent.